Reference signal configuration for coordinated multipoint

ABSTRACT

Coordinated Multipoint (CoMP) involves multiple transmission points or cells coordinating their individual transmissions so that a target user equipment (LTE) experiences enhanced signal reception and/or reduced interference. In order to optimally implement downlink CoMP, a serving cell needs to obtain channel state information (CSI) for the downlink channels from the multiple transmission points to the UE. This disclosure deals with radio resource control (RRC) signaling for configuring the UE to obtain and report CSI for those downlink channels.

PRIORITY CLAIM

This application claims the benefit of priority under 35 U.S.C. 119(e)to U.S. Provisional Patent Application Ser. No. 61/679,627, filed onAug. 3, 2012, which is incorporated herein by reference in its entirety.

BACKGROUND

A major feature of LTE-Advanced (Long Term Evolution-Advanced or LTE-A),as part of Release 10 of the LTE specification by the 3rd GenerationPartnership Project (3GPP), is increased support for CoordinatedMulti-Point (CoMP). In CoMP for the downlink, multiple cells each havinga transmission point (TP) coordinate with one other in transmitting tomobile devices or terminals, referred to as user equipments (UEs) inLTE, so as to result in reduced interference and/or enhanced signalstrength. In order for a set of cooperating cells to employ CoMP intransmitting to a particular target UE, knowledge of the downlinkchannels that exist between the TPs of the cells and the target UE needsto be obtained. Configuring the UE to deliver this information is theprimary concern of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example CoMP system.

FIG. 2 shows an example of joint transmission CoMP.

FIG. 3 shows an example of coordinated scheduling and coordinatedbeamforming CoMP.

FIG. 4 illustrates transmission of CSI configuration information via RRCsignaling.

FIG. 5 is a table by which a CSI-RS configuration number and specificantenna ports are used to map CSI reference signals to specific REs forthe case of a normal cyclic prefix.

FIG. 6 is a table by which a CSI-RS configuration number and specificantenna ports are used to map CSI reference signals to specific REs forthe case of an extended cyclic prefix.

FIG. 7 illustrates an example of the mapping of zero power CSI referencesignals to resource elements using a 16-bit bitmap.

FIG. 8 illustrates an example of the mapping of zero power CSI referencesignals to resource elements using a 32-bit bitmap.

FIG. 9 is a table by which a subframe configuration number defines theperiodicity of CSI reference signals.

DETAILED DESCRIPTION

The following description and the drawings sufficiently illustratespecific embodiments to enable those skilled in the art to practicethem. Other embodiments may incorporate structural, logical, electrical,process, and other changes. Portions and features of some embodimentsmay be included in, or substituted for, those of other embodiments.Embodiments set forth in the claims encompass all available equivalentsof those claims.

CoMP involves multiple transmission points or cells coordinating theirindividual transmissions so that a target UE experiences enhanced signalreception and/or reduced interference. A TP of a cell participating inCoMP may be a base station, referred to as an evolved Node B (eNB) inLTE, or may be a remote radio head (RRH) operated by an eNB. Techniquesfor performing CoMP may be broadly classified into two categories:coordinated scheduling and coordinated beamforming (CS/CB) and jointtransmission (JT). CS/CB involves multiple coordinated cells sharingchannel state information (CSI) for multiple UEs, while the user planedata that is transmitted to a particular UE is transmitted from only oneTP. JT involves multiple coordinated TPs transmitting the same userplane data to a particular UE with appropriate beamforming weights. TPselection (TPS) is a special form of JT where only a single TP transmitsbeamformed user plane data to a particular UE at any one time but the TPthat transmits the user plane data may change at different timeinstances (e.g., between subframes). The primary focus of thisdisclosure is on RRC signaling and configuration for the CoMPmeasurement set and feedback of channel state information.

System Description

FIG. 1 shows an example of a UE D₁ which incorporates a processor 21interfaced to radio-frequency (RF) transceiving circuitry 22 that isconnected to one or more antennas 23. Transmission points TP, throughTP_(N), where N is the number of transmission points in the coordinatingset, are shown as each incorporating a processor 41 interfaced to RFtransceiving circuitry 42 that is connected to a plurality of antennas43. The illustrated components are intended to represent any type ofhardware/software configuration for providing air interfaces for LTEcommunication and for performing the processing functions as describedherein. The transmission point TP₁ is shown as being the serving cellfor the UE D₁ and may be an eNB or other type of base station. Thetransmission points TP₂ through TP_(N) are non-serving CoMP coordinatingcells and may be either base stations or RRHs operated by eNBs. eNBscommunicate with one another via a standardized X2 interface, while RRHsare typically connected to an eNB by an optical fiber link. By means ofthese communications links, the TPs may coordinate their transmissionsand share channel state information received from a UE as describedbelow.

The physical layer of LTE is based upon orthogonal frequency divisionmultiplexing (OFDM) for the downlink and a related technique, singlecarrier frequency division multiplexing (SC-FDM), for the uplink. InOFDM, complex modulation symbols according to a modulation scheme suchas QAM (quadrature amplitude modulation) are each individually mapped toa particular OFDM subcarrier transmitted during an OFDM symbol, referredto as a resource element (RE). The OFDM subcarriers are upconverted toan RF (radio-frequency) carrier before transmission. An RE is thesmallest time-frequency resource in LTE and is uniquely identified byantenna port, sub-carrier position, and OFDM symbol index. Multipleantennas may be used to transmit REs for purposes of beamforming orspatial multiplexing. A group of resource elements corresponding totwelve consecutive subcarriers within a single 0.5 ms slot is referredto as a resource block (RB) or, with reference to the physical layer, aphysical resource block (PRB). Two consecutive slots make up a 1 ms LTEsubframe. Time-frequency resources for the uplink and downlink aredynamically scheduled by the eNB for each UE in terms of RB pairs. LTEalso provides for carrier aggregation whereby multiple RF carriers, eachreferred to as a component carrier (CC), are transmitted in parallelto/from the same UE to provide an overall wider bandwidth andcorrespondingly higher data transmission rate. Carrier aggregation isimplemented in UE-specific manner for each UE, with one CC designated asthe primary carrier or cell and the remaining CCs designated assecondary carriers or cells.

The main purpose of COMP is to deal with the interference problemexperienced by terminals at the edge area of cells. FIGS. 2 and 3illustrate the operation of downlink CoMP for cases of JT and CS/CB,respectively. In FIG. 2, the serving cell TP₁ and the other coordinatingcells TP₂ and TP₃ all jointly transmit to the cell edge terminal UE₁. Bycoherently or non-coherently combining the joint transmissions, thereception power at the terminal is increased. In FIG. 3, thecoordinating cells TP₂ and TP₂ coordinate their antenna weightings andscheduling of downlink transmissions to terminals other than UE₁ inmanner that reduces the interference at UE₁. In order to perform eitherof these functions, as well to select the optimum configuration of TPs,the serving cell needs to know the downlink channel from each TP to thetarget UE. LTE provides reference signals that may be used by a UE toobtain downlink channel state information (CSI) for a transmitting cell,referred to as channel state information reference signals (CSI-RS). TheUE may then feedback the CSI thus obtained to the serving cell in theform of a CSI report.

CS:I-RS are transmitted using REs otherwise allocated to the PDSCH witha configurable periodicity and spanning the entire transmit band. Up toeight CSI-RS, each corresponding to a different antenna port, may betransmitted by a cell. A UE may use the CSI-RS to estimate the channeland produce a CSI report that is fed back to the serving cell via thephysical uplink control channel (PUCCH). A channel state informationreport may include a channel quality indicator (CQI) that represents thehighest modulation and coding scheme that could be used in the channelwithout exceeding a specified error rate, a rank indicator (RI) thatrepresents the number of spatial multiplexing layers that could be usedin the channel, a precoding matrix indicator (PMI) that represents apreferred antenna weighting scheme for transmitting to the UE, and asub-band (SB) indicator that represents the subcarriers preferred by theUE. In order to configure a UE to receive and process reference signalsand to provide appropriate feedback in the form of channel stateinformation reports, the eNB signals the UE using the radio resourcecontrol (RRC) protocol.

The LTE air interface, also referred to as the radio access network(RAN), has a protocol architecture that may be basically described asfollows. In the control plane, the radio resource control (RRC) layer isin control of radio resource usage and communicates with the packet datacompression protocol (PDCP) layer via signaling radio bearers. In theuser plane, the PDCP layer receives radio bearers to which are mapped IP(internet protocol) packets. The PDCP layer communicates with the radiolink control (RLC) layer via the radio bearers, and the RLC layercommunicates with the medium access control (MAC) layer through logicalchannels. The MAC layer communicates via transport channels with thephysical layer (PHY). The primary transport channels used for thetransmission of data, the uplink shared channel (UL-SCH) and downlinkshared channel (DL-SCH), are mapped to the physical uplink sharedchannel (PUSCH) and physical downlink shared channel (PDSCH),respectively, at the physical layer. As illustrated in FIG. 4, an RRCmessage that transmits CSI-RS configuration information from an eNB to aUE originates in the RRC layer of the eNB and, after traversing theprotocol layers, is then transmitted to the UE via the PDSCH. The UEthen processes the message at its corresponding RRC layer.

CSI-RS and Measurement Configuration

Described below are techniques for RRC signaling related to CSImeasurement and feedback configuration for the CoMP measurement set,where the CoMP measurement set is defined as the set of non-zero powerCSI-RS transmitted by particular TPs about which the UE is to performCSI measurements. Based upon those measurements, the UE sends CSIreportsback to the serving cell. The serving cell, based on RSRP (referencesignal received power) as well as other considerations (e.g., SRS(sounding reference signal) measurements), selects a set of CSI-RSs tobe included in the CoMP Measurement set. By means of RRC messages, theserving cell eNB configures the UE to measure CSI-RSs that aretransmitted by particular TPs and send CSIreports based thereon to theeNB. As described below, the configuration involves informing the UE ofthe downlink time-frequency resources used for non-zero power (NZP) andzero power (ZP) CSI-RS that transmitted by one or more TPs. Interferencemeasurement resources (IMR) are also defined for use by the UE indetermining the amount of interference received from both coordinatingcells and neighbor cells not a part of the CoMP coordinating set.Additionally, particular CSI processes are designated for feedback byUE, where each such CSI process includes both a NZP-CSI-RS resource andan interference measurement resource. For each CSI process, the mannerin which. feedback is to be provided by the UE in the form of CSIreportsis also defined. These configurations are captured in a differentinformation elements (IEs) transmitted by RRC signaling such as in anRRCReconfiguration message.

One information element, CSI-RS-Config-r11, defines the CSI-RSconfiguration which includes the set of non-zero power (NZP) CSI-RSresources as well as zero power (ZP) CSI-RS resources and interferencemeasurement (IM) resources. An example of the RRC message expressed inAbstract Syntax Notation.1 (ASN.1) for CSI-RS configuration is asfollows:

 -- ASN1START CSI-RS-Config-r11 ::= SEQUENCE {  csi-RS-ConfigNZP-r11CHOICE {   release NULL,   setup SEQUENCE {   CSI-RS-Identity-NZP-r11::= INTEGER (1.. maxCSIMeas)   antennaPortsCount-r11 ENUMERATED {an1, an2, an4, an8},   resourceConfig-r11 INTEGER (0..31),    subframeConfig-r11 INTEGER(0..154),    p-C-r10 INTEGER (−8..15)   }  } OPTIONAL,  -- Need ON zeroTxPowerCSI-RS-r11 CHOICE {   release NULL,   setup SEQUENCE {   zeroTxPowerResourceConfigList-r11 BIT STRING (SIZE (16)),   resourceConfig-r11 BIT STRING (SIZE (16)),   zeroTxPowerSubframeConfig-r11 INTEGER (0..154)   }  } OPTIONAL  --Need ON } -- ASN1STOPIn the above code fragment, the csi-RS-ConfigNZP-r11 field defines theNZP CSI-RS resource with an identity index (CSI-RS-Identity-NZP-r11),number of antenna ports from which the CSI-RS will be sent(antennaPortsCount-r11) which corresponds to the number of CSI referencesignals, CSI-RS configuration number (resourceConfig-r11), subframeperiodicity and offset (subframeConfig-r11), and the relative powerlevel of CSI-RS (p-C-r10) to power level of PDSCH for which CSI iscalculated. The CSI-RS configuration number and the specific antennaport are used to map the CSI-RS to specific REs using the tables ofFIGS. 5 and 6 for normal and extended cyclic prefixes, respectively (See3GPP TS 36.211 Release 10, tables 6.10.5.2-1 and 6.10.5.2-2).

The zeroTxPowerCSI-RS-r11 field in the above code defines the ZP CSI-RSresources and IM resources. In one embodiment, the interferencemeasurement resources belong to the set of configured ZP CSI-RS. In oneembodiment, the zeroTxPowerResourceConfigList-r11 field for configuringZP CSI-RS is a 16-bit bitmap where each bit corresponds to four REs in asubframe that are to used as a ZP CSI-RS resource. An example of bitmapassignment to ZP CSI-RS resources with four RE granularity is shown inFIG. 7 for a subframe with normal cyclic prefix length bits where eachbit b0 through b9 corresponds to four REs. If higher granularity ZPCSI-RS resources are needed, the length of the bit string can beextended to 32 bits where each bit b0 through b19 corresponds to two REsas shown in FIG. 8.

Since some of the ZP CSI-RSs can be used to improve thesignal-to-interference-plus-noise ratio (SINR) on NZP CSI-RS resourcesof neighboring cells, the interference measurement resources may be asubset of ZP CSI-RS. It is then necessary to indicate a subset of thanthat should be used by the UE for interference measurements. The samebitmap approach can be used to indicate the subset of ZP CSI-RSresources as IM resources where the field resourceConfigList-r11 oflength 16 bits is introduced for the zeroTxPowerCSI-RS-r11 RRC commandas shown in the above code to indicate which of ZP CSI-RS are to be usedfor interference measurement. The indicated interference measurementresources should be a subset of ZP CSI-RS configured byzeroTxPowerResourceConfigList-r11. In another embodiment one ZP CSI-RSresource index in the range of (0 . . . 31) or (0 . . . 15) to indicateeither two or four REs (depending on the embodiment) are signaled toindicate the interference measurement resource, where theresourceConfig-r11 filed corresponds to the CSI-RS configuration numbersdefined in Table 6.10.5.2-1 and 6.10.5.2-2 of TS 36.211 as done for theCSI-RS configuration number (where two or four REs corresponds to two orfour CSI reference signals, respectively). The indicated interferencemeasurement resources should be a subset of ZP CSI-RS configured byzeroTxPowerResourceConfigList-r11.

In another embodiment the NZP CSI-RS resource(s) can be used forinterference measurements in addition or instead of to ZP CSI-RSresources. In this case the interfMeasurementResource-r11 field can beadded to the csi-RS-r11 signaling to indicate whether the UE shouldmeasure the interference on the NZP CSI-RS resource in addition to thechannel measurements. An example of the RRC message in ASN.1 is:

 -- ASN1START CSI-RS-Config-r11 ::= SEQUENCE {  csi-RS-r11 CHOICE {  release NULL,   setup SEQUENCE {    CSI-RS-Identity-NZP-r11 ::=INTEGER (1.. maxCSIMeas)    antennaPortsCount-r11 ENUMERATED {an1, an2,an4, an8},    resourceConfig-r11 INTEGER (0..31),    subframeConfig-r11INTEGER (0..154),    p-C-r11 INTEGER (−8..15),   interfMeasurementResource-r11 BOOL (0,1)   }  } OPTIONAL,  -- Need ON zeroTxPowerCSI-RS-r11 CHOICE {   release NULL,   setup SEQUENCE {   zeroTxPowerResourceConfigList-r11 BIT STRING (SIZE (16)),   interfMeasurementResourceConfigList-r11 (0...31),   zeroTxPowerSubframeConfig-r11 INTEGER (0..154)   }  } OPTIONAL  --Need ON } -- ASN1STOP

Alternatively, the IM resource configuration can be defined using aseparate RRC message and signaled as a combination of aresourceConfig-r11 bitmap (or one ZP CSI-RS resource configuration foranother embodiment) and subframe configuration (subframeConfig-r11),where each IM resource is identified by the CSI-IM-Identity-r11 field.An example of the RRC message is:

CSI-IM-Config-r11 CHOICE {   release NULL,   setup SEQUENCE {    CSI-IM-Identity-r11 INTEGER (0..3),     resourceConfig-r11 BITSTRING (SIZE (16)),     subframeConfig-r11 INTEGER (0..154)   } }OPTIONAL -- Need ON

The subframe configuration is defined in 36.211 by table 6.1.0.5.3-1 asshown in FIG. 9. The subframe configuration period T_(CSI-RS) and thesubframe offset Δ_(CSI-RS) for the occurrence of CSI reference signalsare listed in Table 6.10.5.3-1. The parameter I_(CSI-RS) can beconfigured separately for CSI reference signals for which the UE shallassume non-zero and zero transmission power. Subframes containing CSIreference signals should satisfy the following equation:

(10n _(f) +└n _(s)/2┘−Δ_(CSI-RS))modT _(CSI-RS)=0.

Multiple IM resources may be configured for the UE to enableinterference measurements for multiple interference hypotheses as shownin the following example message:

CSI-IM-List-r11 SEQUENCE {   CSI-IM-Identity-r11 INTEGER (0..3), }OPTIONAL -- Need ON

In another embodiment, implicit indexing (by order of configuration) canbe assumed for CSI-RS-Identity-NZP-r11 and CSI-IM-Identity-r11. In thatcase, configuration of the CSI-RS-Identity-NZP-r11 andCSI-IM-Identity-r11 fields is not necessary for measurement resourceconfigurations.

A CSI process is configured as combination of NZP CSI-RS, IM resource,and measurement subframe set. Each CSI process is identified by a CSIprocess index (csi-Process-Identity-r11 in the example code below) andsubframe set by a csi-MeasSubframeSet-r11. For each CSI process, the UEmeasures the quality of the downlink channel and produces a channelstate information report that, as described above, may include a CQI,RI, PMI, and preferred subbands. The measurement subframe specifiesparticular subframes for which the UE is to measure and report channelquality. Parameters for each CSI process may also include the followingfields: common-RI-Report-r11, common-SB-Report-r11 andcommon-RI-PMI-Report-r11 which indicate re-use of RI, preferredsubbands, and/or RI-PMI from one of CSI processes indicated byref-Csi-Process-Identity-r11. An example message is as follows:

CSI-ProcessList-r11 ::= SEQUENCE {   csi-Process-Identity-r11 INTEGER(1...4),   cellIdx-r11, INTEGER (0..7),   CSI-RS-Identity-NZP-r11,INTEGER (0..3),   CSI-IM-identity-r11, INTEGER (0..3),  csi-MeasSubframeSet-r11, MeasSubframePattern-r10,  common-RI-Report-r11  CHOICE {    release NULL,    setup    ref-Csi-Process-Identity-r11 INTEGER (1...4)   }  common-SB-Report-r11  CHOICE {    release NULL,    setup    ref-Csi-Process-Identity -r11 INTEGER (1...4)   }  common-RI-PMI-Report-r11 CHOICE {    release NULL,    setup    ref-Csi-Process-Identity -r11 INTEGER (1...4)   } }If common-RI-Report-r11, common-SB-Report-r11, common-RI-PMI-Report-r11are configured for a particular CSI, then the rank indicator, preferredset of subbands, and precoding matrix indicator/rank indicator,respectively, are dropped and not transmitted in the channel stateinformation report for that CSI process to save signaling overhead. TheCSI dropping rules for periodic reports on the PUCCH for collisionhandling should take into account that the report is not transmitted andPUCCH resources are vacant. The CSI feedback for the CSI process in thiscase should be calculated conditioned on the report for CSI-processindicated ref-Csi-Process-Identity-r11 associated with reference CSIprocess.

In the above code example, when carrier aggregation is configured, anadditional parameter cellIdx-r11 may be used to indicate the cell onwhich CSI process is defined. Parameters of CSI feedback for multipleCSI processes may be configured for the primary carrier as follows:

CQI-ReportConfigList-r11 ::= SEQUENCE {   csi-Process-Identity-r11INTEGER (1...4),   CQI-ReportConfig-r11 }Parameters of CSI feedback for multiple CSI processes may be configuredfor the secondary carrier as follows:

CQI-ReportConfigSCellList-r11 ::= SEQUENCE {   csi-Process-Identity-r11  INTEGER (1...4),   CQI-ReportConfigSCell-r11 }In another embodiment, the csi-Process-Identity-r11 parameter is uniquewithin each component carrier. In one embodiment, the parametercsi-Process-Identity-r11 is unique across multiple configured carriers.In the latter case, for example, the csi-Process-Identity-r11 parametermay be defined in the range of 0 to 31. CSI reports for each componentcarrier cell may be concatenated in increasing order of CSI processindex followed by CSI report concatenation from multiple componentcarriers in increasing order of cell index. If only one CSI Process canbe configured for a CC (e.g., when no CoMP or a transmission mode notsupporting CoMP is configured for such CC), the value ofcsi-Process-Identity-r11 may be assumed by default, for example, ascsi-Process-Identity-r11=1 (or 0).

It may be desired that the UE only use particular PMIs in its channelstate information reports for particular CSI processes. A set ofrestricted PMIs for associated CSI processes may be communicated fromthe eNB to the UE by an RRC message. An example message that alsoconfigures the transmission mode for the UE is the following code:

AntennaInfoDedicated-r11 ::= SEQUENCE {   transmissionMode-r11ENUMERATED { tm1, tm2, tm3, tm4, tm5, tm6, tm7, tm8-v920, tm9-v1020,tm10, spare7, spare6,   spare5, spare4, spare3, spare2, spare1},  codebookSubsetRestrictionList-r11 SEQUENCE {     csi-Process-Identity-r11 INTEGER (1...4),    codebookSubsetRestriction-r11 BIT STRING OPTIONAL, -- Cond TMX   }  ue-TransmitAntennaSelection CHOICE{     release NULL,     setupENUMERATED {closedLoop, openLoop}   } }The one or more PMIs that are to be restricted for a particular CSIprocess are indicated in the above code fragment by the fieldscodebookSubsetRestriction-r11 and csi-Process-Identity-r11,respectively. Multiple codebookSubsetRestriction-r11's may defined, eachwith an associated CSI process to indicate the restricted PMI or PMIsfor that process.

For CoMP, a new transmission mode (e.g., TM10) is defined which supportsCSI reports for one or more CSI processes and uses random UE-specificreference signal based precoding for fallback mode. The new transmissionmode uses DCI based on Format 2D with PDSCH RE mapping and quasico-location (PQI) field to inform the UE about the transmitting point orset of transmitting points.

Aperiodic channel-state reports are delivered by the UE when explicitlyrequested to do so by the network using a flag in the CSI request fieldof the DCI carried by the PDCCH or enhanced PDCCH. The CSI request fieldis a two-bit field that when set to “00” indicates no CSI report isrequested as described in the LTE specifications (See 3GPP TS 36.213).When the CSI request field is set to “10” or “11,” it indicates that aCSI report is triggered for one of two alternative sets of CSI processesas configured by higher layers. RRC signaling may be used to tell the UEwhich CSI processes are to be reported on when a flag is detected in theCSI request field. An example RRC message defines aperiodic feedbackaperiodicCSI-Trigger-r11 as follows:

CQI-ReportAperiodic-r11 ::= CHOICE {  release   NULL,  setup   SEQUENCE{    cqi-ReportModeAperiodic-r11    CQI-ReportModeAperiodic,   aperiodicCST-Trigger-r11    SEQUENCE {      trigger1-r11    BITSTRING (SIZE (15)),      trigger2-r11    BIT STRING (SIZE (15))    }OPTIONAL  -- Need OR  } }The aperiodicCSI-Trigger-r11 field in the above code indicates for whichCSI processes the aperiodic CSI report is triggered when one or more CSIprocesses are configured. The trigger1-r11 field is a bit string thatcorresponds to the CSI request field “10,” and the trigger2-r11 field isa bit string that corresponds to the CSI request field “11.” Each bit inthe bit strings corresponds to a particular CSI process. For example,bit 0 in the bit string may corresponds to the CSI process withCSIProcessId=0, and bit 1 in the bit string corresponds to the CSIprocess with CSIProcessId=1 and so on. Each bit has either value 0 tomean that no aperiodic CSI report is triggered for that CSI process orvalue 1 to mean that the aperiodic CSI report is triggered. In the abovecode example, the trigger1-r11 and trigger2-r11 are 15-bit bit strings,meaning that at most 15 bits can be set to value 1 in each bit string torequest 15 CSI reports. The size of bit strings should depends on themaximum number of CSI processes to be configured for a UE across allcarriers when CoMP is used combined with carrier aggregation based on UEcapability. In the above example, the bit string size of 15 could beused for three CSI processes configured on each of five carriers. Inanother embodiment, 20-bit indexes could be used to allow at most 20bits to be set to value 1 in the bit string if a maximum of four CSIprocesses are allowed per carrier. Also, in other embodiments, moretrigger fields can be defined. For example, trigger1-r11, trigger2-r11,trigger3-r11, etc. could be included in the RRC message with more bitsbeing correspondingly allocated for the CSI request fields in the DCI.Also, in one embodiment, for the PDCCH common search space, the CSIrequest field is one bit and is used to trigger the CSI process with thesmallest CSI process index.

Example Embodiments

In example embodiments, a base station for acting as an eNB and a UEboth include a transceiver for providing an LTE air interface andprocessing circuitry connected to the transceiver. The eNB is configuredto act as a serving cell to the UE and act as one of a plurality ofcooperating coordinated multi-point (CoMP) transmission points (TPs) forthe UE. The processing circuitry of the UE is to receive RRC messagingtransmitted by the eNB according to any or all of the following exampleembodiments. The processing circuitry of the eNB may be to configure theUE to receive channel state information (CSI) reference signals (CSI-RS)transmitted from one or more of the cooperating TPs by transmitting aradio resource control (RRC) configuration message to the UE, whereinthe RRC configuration message includes a set of indexed non-zero power(NZP) CSI-RS resources that are to be included in a CoMP measurementset, a set of zero power (ZP) CSI-RS resources, and interferencemeasurement (IM) resources for use by the UE making interferencemeasurements. The RRC message may further include subframe configurationperiods including subframe offsets for separately specifying theperiodicity of the NZP CSI-RS, IM resources, and the ZP CSI-RS. The IMresources may be a set of indexed IM resources and may be a subset ofthe set of ZP CSI-RS resources. The set of ZP CSI-RS resources may betransmitted as a bitmap (e.g., 16-bit) with each bit corresponding to aparticular CSI-RS configuration that is to be regarded as having zerotransmission power and the set of IM resources may be configured with abitmap indicating which of the ZP-CSI resources are to be used forinterference measurements. The set of IM resources may be configuredwith a bitmap (e.g., 16-bit) with each bit corresponding to a particulargroup of four resource elements (REs) belonging to the set of ZP CSI-RSor configured with a bitmap (e.g., 32-bit) with each bit correspondingto a particular resource element (RE) pair belonging to the set of ZPCSI-RS resources. The set of IM resources may be configured as aparticular CSI-RS configuration with four antenna ports whose resourcesare to be used by the UE for interference measurement or is configuredas a particular CSI-RS configuration with two antenna ports whoseresources are to be used by the UE for interference measurement. Theprocessing circuitry may be to transmit explicit indexes of the NZPCSI-RS resources in the RRC message or to implicitly indicate theindexes of the NZP CSI-RS resources by their order of configuration inthe RRC message. The RRC configuration message may include an indicationthat one or more particular NZP CSI-RS resources is an interferencemeasurement (IM) resource for use by the UE in making interferencemeasurements. The processing circuitry may be to transmit an RRC messageincluding configuration of multiple indexed IM resources to enableinterference measurements by the UE for multiple interferencehypotheses. The processing circuitry may be to transmit explicit indexesof the IM resources in the RRC message or to implicitly indicate indexesof the IM resources by their order of configuration in the RRC message.The processing circuitry may be to transmit explicit indexes of the NZPCSI-RS resources in the RRC message or to implicitly indicate indexes ofthe NZP CSI-RS resources by their order of configuration in the RRCmessage. The processing circuitry may be to configure one or moreindexed CSI processes via RRC messaging, where each CSI process is as acombination of a NZP CSI-RS resource, an IM resource, and a measurementsubframe set specifying for which subframes CSI is to be reported by theUE. Two or more CSI processes may be configured such that CSI is to bereported using a common rank indicator (RI), a common precoding matrixindicator (PMI), or a common preferred set of subbands. The processingcircuitry may be to, if carrier aggregation is configured, configure theone or more indexed CSI processes with a cell index indicating for whichcomponent carrier the CSI process is defined. The CSI process index maybe unique across multiple component carriers or unique within eachconfigured component carrier. The CSI process index may be equal to adefault value when only one CSI process on the component carrier or atransmission mode not supporting CoMP can be configured. The processingcircuitry may be to configure the UE to transmit CSI reportsconcatenated in increasing order of CSI process index and, for each CSIprocess index when carrier aggregation is configured, concatenated inincreasing order of cell index. The processing circuitry may be toconfigure each CSI process with a set of restricted PMIs for reportingCSI. The processing circuitry may be to configure aperiodic CSI processsets via an RRC message with a bit string where each bit of the bitstring corresponds to a CSI process index and indicates whether or notCSI is to be reported by the UE when a corresponding trigger isreceived.

The embodiments as described above may be implemented as methods foroperation and/or in various hardware configurations that may include aprocessor for executing instructions that perform the methods. Suchinstructions may be contained in a suitable storage medium from whichthey are transferred to a memory or other processor-executable medium.

The subject matter has been described in the context of an LTE network.Except where inconsistencies would arise, the subject matter could beused in other types of cellular networks with references to a UE and eNBreplaced by references to a terminal and base station, respectively.

The subject matter has been described in conjunction with the foregoingspecific embodiments. It should be appreciated that those embodimentsmay also be combined in any manner considered to be advantageous. Also,many alternatives, variations, and modifications will be apparent tothose of ordinary skill in the art. Other such alternatives, variations,and modifications are intended to fall within the scope of the followingappended claims.

The Abstract is provided to comply with 37 C.F.R. Section 1.72(b)requiring an abstract that will allow the reader to ascertain the natureand gist of the technical disclosure. It is submitted with theunderstanding that it will not be used to limit or interpret the scopeor meaning of the claims. The following claims are hereby incorporatedinto the detailed description, with each claim standing on its own as aseparate embodiment.

What is claimed is:
 1. A user equipment (UE) device for operating in aLong Term Evolution (LTE) network, comprising: a transceiver forproviding an LTE air interface to an evolved Node B (eNB); and,processing circuitry connected to the transceiver and to: receive aradio resource control (RRC) configuration message from the eNB thatconfigures the UE to receive channel state information (CSI) referencesignals (CSI-RS) transmitted from one or more coordinated multi-point(CoMP) transmission points (TPs); wherein the RRC configuration messageincludes a set of indexed non-zero power (NZP) CSI-RS resources that areto be included in a CoMP measurement set, a set of zero power (ZP)CSI-RS resources, and interference measurement (IM) resources for use bythe UE in making interference measurements.
 2. The device of claim itwherein the set of IM resources is a subset of the set of ZP CSI-RSresources.
 3. The device of claim 2 wherein the set of ZP CSI-RSresources is transmitted as a 16-bit bitmap with each bit correspondingto a particular CSI-RS configuration that is to be regarded as havingzero transmission power and further wherein the set of IM resources isconfigured with a bitmap indicating which of the ZP-CSI resources are tobe used for interference measurements.
 4. The device of claim 1 whereinthe RRC configuration message further includes an indication that one ormore particular NZP CSI-RS resources is an interference measurement (IM)resource for use by the UE in making interference measurements.
 5. Thedevice of claim 1 wherein the processing circuitry is to receive RRCconfiguration messaging that configures one or more indexed CSIprocesses, where each CSI process is as a combination of a NZP CSI-RSresource, IM resource, and measurement subframe set specifying for whichsubframes set CSI is to be reported by the UE.
 6. The device of claim 5wherein the processing circuitry is to receive RRC configurationmessaging that configures two or more CSI processes such that CSI is tobe reported using a common rank indicator (RI), a common precodingmatrix indicator (PMI), or a common preferred set of subbands.
 7. Thedevice of claim 1 wherein the processing circuitry is to receive RRCconfiguration messaging that configures one or more indexed CSIprocesses via RRC messaging, where each CSI process is as a combinationof a NZP CSI-RS resource, IM resource, and measurement subframe setspecifying for which subframes set CSI is to be reported by the UE. 8.The device of claim 7 wherein the processing circuitry is to receive RRCconfiguration messaging that configures two or more CSI processes suchthat CSI is to be reported using a common rank indicator (RI), a commonprecoding matrix indicator (PMI), or a common preferred set of subbands.9. A base station for acting as an evolved node B (eNB) in a Long TermEvolution (LTE) network, comprising: a transceiver for providing an LTEair interface to a plurality terminals; and, processing circuitryconnected to the transceiver and to: act as a serving cell to a userequipment (UE) and act as one of a plurality of cooperating coordinatedmulti-point (CoMP) transmission points (TPs) for the UE; configure theUE to receive channel state information (CSI) reference signals (CSI-RS)transmitted from one or more of the cooperating TPs by transmitting aradio resource control (RRC) configuration message to the UE; whereinthe RRC configuration message includes a set of indexed non-zero power(NZP) CSI-RS resources that are to be included in a CoMP measurementset, a set of zero power (ZP) CSI-RS resources, and a set of indexedinterference measurement (IM) resources tzar use by the UE in makinginterference measurements; and, wherein the set of IN resources is asubset of the set of ZP CSI-RS resources.
 10. The base station of claim9 wherein the RRC message further includes subframe configurationperiods including subframe offsets for separately specifying theperiodicity of the NZP CSI-RS, IM resources, and the ZP CSI-RS.
 11. Thebase station of claim 9 wherein the set of ZP CSI-RS resources istransmitted as a bitmap with each bit corresponding to a particularCSI-RS configuration that is to be regarded as having zero transmissionpower and further wherein the set of IM resources is configured with abitmap indicating which of the ZP-CSI resources are to be used forinterference measurements.
 12. The base station of claim 11 wherein theset of IM resources is configured with a bitmap with each bitcorresponding to a particular group of four resource elements (REs)belonging to the set of ZP CSI-RS or is configured with a bitmap witheach bit corresponding to a particular resource element (RE) pairbelonging to the set of ZP CSI-RS resources.
 13. The base station ofclaim 9 wherein the set of IM resources is configured as a particularCSI-RS configuration with four antenna ports whose resources are to beused by the UE for interference measurement or is configured as aparticular CSI-RS configuration with two antenna ports whose resourcesare to be used by the UE for interference measurement.
 14. The basestation of claim 9 wherein the processing circuitry is to transmitexplicit indexes of the NZP CSI-RS resources in the RRC message.
 15. Thebase station of claim 9 wherein the processing circuitry is toimplicitly indicate the indexes of the NZP CSI-RS resources by theirorder of configuration in the RRC message.
 16. A base station for actingas an evolved node B (eNB) in a Long Term Evolution (LTE) network,comprising: a transceiver for providing an LTE air interface; andprocessing circuitry connected to the transceiver and to: act as aserving cell to a user equipment (UE) and act as one of a plurality ofcooperating coordinated multi-point (CoMP) transmission points (TPs) forthe UE; configure the UE to receive channel state information (CSI)reference signals (CSI-RS) transmitted from one or more of thecooperating TPs by transmitting a radio resource control (RRC)configuration message to the UE; wherein the RRC configuration messageincludes a set of indexed non-zero power (NZP) CSI-RS resources that areto be included in a CoMP measurement set and a set of zero power (ZP)CSI-RS resources; wherein the RRC configuration message further includesan indication that one or more particular NZP CSI-RS resources is aninterference measurement (IM) resource for use by the UE in makinginterference measurements.
 17. The base station of claim 16 wherein theprocessing circuitry is to transmit an RRC message includingconfiguration of multiple indexed IM resources for enabling interferencemeasurements by the UE for multiple interference hypotheses.
 18. Thebase station of claim 17 wherein the processing circuitry is to transmitexplicit indexes of the IM resources in the RRC message.
 19. The basestation of claim 17 wherein the processing circuitry is to implicitlyindicate indexes of the IM resources by their order of configuration inthe RRC message.
 20. The base station of claim 16 wherein the processingcircuitry is to transmit explicit indexes of the NZP CSI-RS resources inthe RRC message.
 21. The base station of claim 16 wherein the processingcircuitry is to implicitly indicate indexes of the NZP CSI-RS resourcesby their order of configuration in the RRC message.
 22. A method foroperating an evolved node B (eNB) in a Long Term Evolution (LTE)network, comprising: acting as a serving cell to a user equipment (UE)and acting as one of a plurality of cooperating coordinated multi-point(CoMP) transmission points (TPs) for the UE; configuring the UE toreceive channel state information (CSI) reference signals (CSI-RS)transmitted from one or more of the cooperating TPs by transmitting aradio resource control (RRC) configuration message to the UE; whereinthe RRC configuration message includes a set of indexed non-zero power(NZP) CSI-RS resources that are to be included in a CoMP measurementset, a set of zero power (ZP) CSI-RS resources, and an indexed set ofinterference measurement (IM) resources for use by the UE in makinginterference measurements; and, configuring one or more indexed CSIprocesses via RRC messaging, where each CSI process is as a combinationof a NZP CSI-RS resource, and IM resource, and a measurement subframeset specifying for which subframes CSI is to be reported by the UE. 23.The method of claim 22 further comprising configuring two or more CSIprocesses such that CSI is to be reported using a common rank indicator(RI), a common precoding matrix indicator (PMI), or a common preferredset of subbands.
 24. The method of claim 22 further comprising, ifcarrier aggregation is configured, configuring the one or more indexedCSI processes with a cell index indicating for which component carrierthe CSI process is defined.
 25. The method of claim 24 wherein the CSIprocess index is unique across multiple component carriers.
 26. Themethod of claim 24 wherein the CSI process index is unique within eachconfigured component carrier.
 27. The method of claim 24 wherein the CSIprocess index is equal to a default value when only one CSI process onthe component carrier or a transmission mode not supporting CoMP can beconfigured.
 28. The method of claim 22 further comprising configuringthe UE to transmit CSI reports concatenated in increasing order of CSIprocess index and, for each CSI process index when carrier aggregationis configured, concatenated in increasing order of cell index.
 29. Themethod of claim 22 further comprising configuring each CSI process witha set of restricted Mils for reporting CSI.
 30. The method of claim 22further comprising configuring aperiodic CSI process sets via an RRCmessage with a bit string where each bit of the bit string correspondsto a CSI process index and indicates whether or not CSI is to bereported by the UE when a corresponding trigger is received.